A Database Management System consists of a set of tools used to develop and manage a database. The presently described system utilizes DMSII, which is a Database Management System available on a Unisys Corporation's ClearPath HMP NX, and also the Unisys A-Series systems. A background for the Unisys DMSII systems is available in a publication of the Unisys Corporation, Document 8807 6625 000, entitled “Getting Started With DMSII” and published in September 1997 by the Unisys Corporation. The DMSII Utilities provide database backup and recovery capability for the entire database or for partial databases. The background operations of the DMSII utility enhancements are published in a Unisys Corporation publication Document 98037/4 and entitled “DMSII Utility Enhancements” as published on Mar. 31, 1999.
Database Management Systems are used by many large and small businesses such as airline reservation systems, financial institutions, retail chains, insurance companies, utility companies and government agencies. The present Database Management System (DMS) in its form designated as DMSII is used to build database structures for items of data according to some appropriate logical model, such as relational, hierarchical, or network. Further, the Database Management System is used to manage the database structures and keep the structures in some other stable order while various application programs may be retrieving or changing the data. The present embodiment of DMSII has a Data Definition Language designated as Data And Structure Definition Language (DASDL).
There are various tasks that are performed in database management and these involve (i) monitoring and optimizing database performance; (ii) the use of database control for monitoring multi-program database access; (iii) the function of the data integrity and safety done by integrity checking and preventing access to the same data by multiple applications occurring at the same time; (iv) the function of defining data structures and the data fields within them, including the function of modifying data structures; (v) data access operations and developing an application program to retrieve data or to change data; (vi) the function of data shareability to provide multi-program access without conflicts and provide database definitions to the application program; (vii) in database and data security, to prevent unauthorized database access; (viii) ensuring independence of application programs from certain data changes and preventing the revision of application programs every time a structure changes; (ix) in database and data recovery, performing the resumption of database operations after an interruption; (x) tracking data changes by keeping a record of every change made to the data; (xi) for data change integrity, ensuring that update changes are applied to, or removed from, the database in their entirety; (xii) providing a recent copy of the database as a reserve by backing-up the database and storing copies of audit files and all other database files; (xiii) providing for database scalability by growing or shrinking the database according to the ongoing needs at the time.
The DMSII provides standard software files that perform services and operations for all the databases connected to the system's Enterprise Server. This enables a viewing of a list of all these files on the user terminal.
A Database Administrator (DBA) is used to keep the database running smoothly and to enforce the rules for data integrity and security.
In environments where Unisys ClearPath servers are used, systems from several other hardware and software vendors may be found. Many of the business databases on these other systems are based on the Relational Database Model. The need for database administrators (DBA) to leverage their time as efficiently as possible has lead the database industry to provide some ease-of-use features to their products. For example, a DMSII Database Operations Center (DOC) provides a graphical user interface (GUI) for the Enterprise Database Server in its Extended Edition.
In order to provide flexibility in database operations, it is not only desirable to convert relational schemas to hierarchical schemas, but also to provide the ability to convert hierarchical schemas to functionally equivalent relational schemas.